Stereoselective synthesis of protectin D1: A potent anti-inflammatory and proresolving lipid mediator

Article abstract of DOI:10.1039/c3ob41902a

A convergent stereoselective synthesis of the potent anti-inflammatory, proresolving and neuroprotective lipid mediator protectin D1 (2) has been achieved in 15% yield over eight steps. The key features were a stereocontrolled Evans-aldol reaction with Nagao's chiral auxiliary and a highly selective Lindlar reduction of internal alkyne 23, allowing the sensitive conjugated E,E,Z-triene to be introduced late in the preparation of 2. The UV and LC/MS-MS data of synthetic protectin D1 (2) matched those obtained from endogenously produced material.

Full text of DOI:10.1039/c3ob41902a

Volume 12 Number 3 21 January 2014 Pages 385–542
Organic &
Biomolecular
Chemistry
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ISSN 1477-0520
PAPER
T. V. Hansen et al.
Stereoselective synthesis of protectin D1: a potent anti-inflammatory and
proresolving lipid mediator

Organic &
Biomolecular Chemistry
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PAPER
Stereoselective synthesis of protectin D1: a potent
anti-inflammatory and proresolving lipid mediator†
M. Aursnes,a J. E. Tungen,a A. Vik,a J. Dallib and T. V. Hansen*a
Cite this: Org. Biomol. Chem., 2014,
12, 432
A convergent stereoselective synthesis of the potent anti-inflammatory, proresolving and neuroprotective
lipid mediator protectin D1 (2) has been achieved in 15% yield over eight steps. The key features were a
stereocontrolled Evans-aldol reaction with Nagao’s chiral auxiliary and a highly selective Lindlar reduction
of internal alkyne 23, allowing the sensitive conjugated E,E,Z-triene to be introduced late in the prepa-
ration of 2. The UV and LC/MS–MS data of synthetic protectin D1 (2) matched those obtained from
endogenously produced material.
Received 19th September 2013,
Accepted 31st October 2013
DOI: 10.1039/c3ob41902a
www.rsc.org/obc
Introduction
Polyunsaturated fatty acids (PUFAs), such as docosahexaenoic
acid (1, DHA), play a major role in the physiology of living
organisms.1 Recent efforts by the Serhan research group have
established that DHA (1) is a substrate for the biosynthesis of
several potent anti-inflammatory proresolving mediators, such
as protectin D1 (2),2 maresin 1,3 resolvin D1 and resolvin
D3.2a,4 All of these compounds have enabled new research
areas related to many disease states associated with inflam-
mation.5 It was reported that protectin D1 (2) is biosynthesized
from DHA (1) via a lipoxygenase-mediated pathway that con-
verts 1 by 15-lipoxygenase (15-LO) to the 17S-hydroperoxide
intermediate (3), which is rapidly converted into the 16,17-
epoxide (4), followed by enzymatic hydrolysis to the anti-
inflammatory and proresolving oxygenated lipid 2 (Fig. 1).6
This compound has been reported to exhibit strong in vivo
protective activity in several inflammatory6 as well as many
other disease models.7–10 For example, the oxygenated poly-
unsaturated fatty acid 2 protects the retina and the brain from
oxidative stress with very potent agonist activities.7 It is note-
worthy that 2 was observed to be several orders of magnitude
more potent in vivo than its precursor DHA.2c Moreover,
additional biological effects have recently been reported for
this C22-oxygenated metabolite.11 Hence, protectin D1 (2) is
Fig. 1 Biosynthesis of protectin D1 (2).
very interesting as a lead compound for the development of
potential new anti-inflammatory drugs.12 The prefix neuro
is added when this oxygenated PUFA is formed by neural
tissues.2a As of today, two syntheses of protectin D1 (2) have
appeared.6,13 In connection with our interest in the synthesis of
biologically active PUFA-derived natural products,14 as well as the
many interesting biological activities of protectin D1 (2), we
decided to prepare the DHA derived product 2. A common struc-
tural feature for several of the lipid mediators isolated by the
Serhan group2–4 is the chemically unstable E,E,Z-triene connected
to either one or two secondary allylic alcohols. In the retrosyn-
thetic analysis of 2, Fig. 2, the aldehyde 6 is a key intermediate.
aSchool of Pharmacy, Department of Pharmaceutical Chemistry, University of Oslo,
PO Box 1068 Blindern, N-0316 Oslo, Norway. E-mail: t.v.hansen@farmasi.uio.no
bCenter for Experimental Therapeutics and Reperfusion Injury, Department of
Anesthesiology, Perioperative and Pain Medicine, Harvard Institutes of Medicine,
Brigham and Women’s Hospital and Harvard Medical School, Boston,
Massachusetts 02115, USA
†Electronic supplementary information (ESI) available: Additional experimental
procedures and characterization data, 1H-, 13C-NMR, HRMS, LC-MS/MS and
UV/VIS spectra as well as chromatograms of HPLC analyses. See DOI:
10.1039/c3ob41902a
432 | Org. Biomol. Chem., 2014, 12, 432–437
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1
ratio as determined by HPLC and H NMR analyses. We also
investigated reactions using thiazolidinones 9b and 9c, with
the phenyl and the benzyl group, respectively, which afforded
16b and 16c with lower diastereoselectivity (4.5 : 1 and 9.8 : 1).
Purification by chromatography yielded diastereomeric pure
16a in 86% isolated yield. Protection of the alcohol functional-
ity in 16a to compound 17 was achieved using standard con-
ditions.20 Then DIBAL-H-reduction of 17 in CH2Cl2 at −78 °C
afforded the sensitive aldehyde 6 (Scheme 1).
Next, the Wittig-salt 7 was synthesized. The dianion of
4-pentynoic acid (11) in HMPA,21 prepared by treatment with
excess n-BuLi, was reacted with ethylene oxide (10). This
afforded 7-hydroxy-hept-4-ynoic acid which was directly esteri-
fied to 18 (MeOH, catalytic H2SO4), see Scheme 2. Reduction
of the internal alkyne in 18 using the Lindlar reaction gave (Z)-
methyl 7-hydroxyhept-4-enoate (19) with high stereochemical
purity as determined by 1H NMR analyses. Then an Appel reac-
tion22 provided the iodide 20 which was treated with PPh3 in
acetonitrile to provide the Wittig-salt 7 in a total yield of 42%
from 11. Conditions for the Z-stereoselective Wittig reaction
between the key aldehyde 6 and the salt 7 were then investi-
gated. Different bases, i.e. LiHMDS, KHMDS, NaHMDS, temp-
eratures as well as altering the concentrations of 6 and 7, with
or without different amounts of HMPA in THF, all resulted in
lower Z-selectivity. The best result was obtained when aldehyde
6 and the ylide of 7, the latter obtained after treatment with
NaHMDS in THF, were reacted at −78 °C. This afforded the
bromo-E,E,Z,Z-tetraene ester 21 (Scheme 2).
Chromatographic purification on silica gel yielded stereo-
chemically pure product 21 (HPLC, 1H-NMR) in 47% yield over
two steps. Then alkyne 5 was reacted with 21 in a Sonogashira
reaction23 at ambient temperature in the presence of Pd-
(PPh3)4 and CuI using diethyl amine as a solvent. This
afforded the bis-hydroxyl-protected methyl ester 22 in 95%
yield. Deprotection of the two TBS-groups in 22 was achieved
with an excess of five equivalents of TBAF in THF at 0 °C to
Fig. 2 Retrosynthetic analysis of protectin D1 (2).
Results and discussion
Our synthesis of 2 commenced with the preparation of 5,
essentially as previously reported,15 from 1-butyne (12) and
THP-protected (R)-glycidol 13 (Scheme 1).
Aldehyde 8 was prepared by a slightly modified and
improved literature protocol.16 Commercially available pyridi-
nium-1-sulfonate (14) was treated with aqueous potassium
hydroxide at −20 °C to yield glutaconaldehyde potassium salt
15 that was transformed further with the Br2/PPh3 complex to
(2E,4E)-5-bromopenta-2,4-dienal (8) in 41% yield over the two
steps. This sensitive aldehyde was then reacted with thiazolidi-
none 9a, developed by Nagao and co-workers,17 in an Evans-
aldol18 type reaction using conditions developed by Olivo and
co-workers (TiCl4, Et(i-Pr)2N, CH2Cl2, −78 °C).19 This smoothly
produced the intermediate 16a in a 15.3 : 1 diastereomeric
Scheme 1 Synthesis of alkyne 5 and aldehyde 6.
Scheme 2 Synthesis of ester 21.
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Scheme 3 Synthesis of protectin D1 (2).
afford 81% yield of the diol 23.24 The internal conjugated
alkyne in 23 was reduced to the methyl ester 24 in 65% yield
after chromatographic purification on silica. A modified
Lindlar hydrogenation reaction25 produced triene 24 with high
stereoselectivity, while the diimide reduction26 or the standard
Lindlar hydrogenation reaction27 of 23 failed to give a high
conversion to 24. The Boland reduction28 gave in our hands a
large amount of elimination of water from 23. Finally, lenient
saponification of the methyl ester 24 at 0 °C with dilute
aqueous LiOH in methanol followed by mild acidic work-up
(aqueous NaH2PO4) afforded a 78% yield of protectin D1 (2) in
the last step (Scheme 3).
The chemical purity of synthetic 2 and 24 was determined
to be >95% and >98%, respectively, by HPLC analyses (see
ESI†). The UV spectrum of synthetic protectin D1 (2) showed
absorbance peaks (λMmaeOx H) at 262, 271 and 282 nm, which is in
excellent agreement with the literature.6 In order to obtain evi-
dence that synthetic 2 and 24 matched that of authentic pro-
tectin D1 (2), protectin D1 (2) was obtained from endogenous
murine self-resolving exudates.29 Fig. 3 shows that the syn-
thetic 2 was matched with endogenously produced 2.
Fig. 3 HPLC chromatograms obtained from the matching experiments.
Authentic protectin D1 (2) from self-resolving peritoneal inflammatory
exudates matched synthetic material protectin D1 (2). Selected ion chro-
matograms (m/z 359–153) depicting (A) authentic protectin D1 (2),
marked as PD1, obtained from mice injected with Escherichia coli (105
CFU) and exudates collected at 12 h; (B) synthetic protectin D1 (2) and
(C) coinjection of protectin D1 (2) from self-resolving inflammatory exu-
dates with synthetic material protectin D1 (2). Figures (A)–(C) are repre-
sentative HPLC chromatograms (n = 4).
D1 (2). The chromatographic properties of synthetic 2 and the
free acid of 24, the latter obtained by hydrolysis with aqueous
LiOH in THF,6 were matched with data of endogenously formed
protectin D1 (2). These results demonstrated that hydrolyzed 24
co-elutes with authentic 2. Furthermore, the MS–MS spectra for
both the free acid obtained from 24 and biosynthesized 2 dis-
played essentially identical MS–MS fragmentation spectra (see
ESI†). Our NMR spectral data of synthetic 2 were in accord with
those published by Petasis, Serhan and co-workers,13b but not
with the spectra published by others.13a
In Fig. 3A authentic protectin D1 (2) obtained in vivo from
exudates is displayed amongst its stereoisomers.30 Fig. 3B
shows the chromatographic behaviour of endogenously pro-
duced 2 (TR = 13.2 min) and Fig. 3C demonstrates that syn-
thetic 2 co-elutes with endogenous 2. In addition, the MS–MS
spectra for both biosynthesized 2 and synthetic 2 displayed
essentially identical MS–MS fragmentation spectra with the
following fragments assigned: m/z 359 = M-H, m/z 341 = M-H-
H2O, m/z 323 = M-H-2H2O, m/z 315 = M-H-CO2, m/z 297 = M-H-
H2O-CO2, m/z 279 = M-H-2H2O-CO2, m/z 243 = 261-H2O, m/z
199 = 261-H2O-CO2, m/z 188 = 206-H2O, m/z 135 = 153-H2O,
m/z 121 = 181-H2O-CO2, m/z 109 = 153-CO2 (see ESI†). Similar
results were also obtained when synthetic ester 24 was hydro-
lysed to the acid 2 and compared with authentic protectin
Conclusions
In summary, the potent endogenously produced lipid
mediator protectin D1 (2) was prepared in eight steps and in
15% yield from the known aldehyde 8 in a convergent manner.
Our synthesis of 2 compares well with those previously
reported with respect to yields and simplicity, affording multi-
mg quantities of this potent and biologically interesting
natural product. The synthetic material displayed identical
chromatographic properties with endogenously produced pro-
tectin D1 (2). Further in vivo biological studies are ongoing
and will be reported elsewhere.
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−78 °C and then stirred for 5 min at 0 °C. Aldehyde 6
(prepared from DIBAL-H reduction of 17 as described above)
was added at −78 °C. The solution was allowed to slowly warm
up to room temperature in the dry ice/acetone bath for 24 h
Experimental
(R,4E,6E)-7-Bromo-3-((tert-butyldimethylsilyl)oxy)hepta-
4,6-dienal (6)
Aldehyde 6 was prepared by a DIBAL-H reduction of the before it was quenched with phosphate buffer (10 mL, pH =
protected thiazolidinethione 17 according to the procedure of 7.2). Et2O (15 mL) was added and the phases were separated.
Olivo et al.19b All spectroscopic and physical data were in full The aqueous phase was extracted with Et2O (2 × 15 mL) and
agreement with those reported in the literature.19b [α]D20 = 31.5 the combined organic layers were dried (Na2SO4), before it was
(c = 0.2, CHCl3); 1H NMR (300 MHz, CDCl3) δ 9.75 (t, J = concentrated in vacuo. The crude product was purified by
2.2 Hz, 1H), 6.69 (dd, J = 13.4, 10.8 Hz, 1H), 6.33 (d, J = column chromatography on silica (hexanes–EtOAc 95 : 5) to
13.6 Hz, 1H), 6.16 (ddd, J = 15.2, 10.6, 1.3 Hz, 1H), 5.75 (ddd, afford the title compound 21 as a yellow oil. Yield: 217 mg
J = 15.3, 5.9, 0.8 Hz, 1H), 4.66 (dd, J = 6.8, 5.5 Hz, 1H), (47% for two steps starting from 17); TLC (hexanes–EtOAc
1
2.75–2.41 (m, 2H), 0.87 (s, 9H), 0.06 (s, 3H), 0.04 (s, 3H); 95 : 5, CAM stain): Rf = 0.29; [α]2D0 = −9.4 (c = 0.1, MeOH); H
13C NMR (75 MHz, CDCl3) δ 201.2, 136.6, 136.1, 127.6, 109.6, NMR (400 MHz, CDCl3) δ 6.68 (dd, J = 13.4, 10.9 Hz, 1H), 6.27
68.5, 51.4, 25.9, 14.3, −4.2, −4.9.
(d, J = 13.5 Hz, 1H), 6.09 (dd, J = 15.2, 10.8 Hz, 1H), 5.72 (dd,
J = 15.2, 5.8 Hz, 1H), 5.48–5.32 (m, 4H), 4.16 (q, J = 6.0 Hz, 1H),
3.67 (s, 3H), 2.84–2.73 (m, 2H), 2.38–2.35 (m, 4H), 2.35–2.21
(m, 2H), 0.89 (s, 9H), 0.05 (s, 3H), 0.02 (s, 3H); 13C NMR
(R,4E,6E)-7-Bromo-3-hydroxy-1-((S)-4-isopropyl-
2-thioxothia-zolidin-3-yl)hepta-4,6-dien-1-one (16a)
The (R)-aldol product 16a was prepared in 86% yield from (101 MHz, CDCl3) δ 173.6, 138.0, 137.1, 129.9, 129.4, 128.0,
dienal 8 and the auxiliary 9a according to the procedure of 126.7, 125.6, 108.3, 72.6, 51.7, 36.3, 34.1, 26.0 (3C), 25.9, 23.0,
Olivo and coworkers.19a The diastereomeric ratio (15.3 : 1) on 18.4, −4.4, −4.6. HRMS (TOF ES+): Exact mass calculated for
the crude product was determined by HPLC analysis (Eclipse C21H35O3Si79BrNa [M + Na]+: 465.1436, found 465.1431.
XDB-C18, MeOH–H2O 70 : 30, 1.0 mL min−1, tr(minor) =
8.65 min and tr(major) = 10.85 min). All spectroscopic and
physical data were in full agreement with those reported in the
literature.19a [α]D20 = 271.3 (c = 0.13, CHCl3); 1H NMR (300 MHz,
Methyl (4Z,7Z,10R,11E,13E,17S,19Z)-10,17-bis((tert-butyl-
di-methylsilyl)oxy)docosa-4,7,11,13,19-pentaen-15-ynoate (22)
CDCl3) δ 6.72 (dd, J = 13.5, 10.8 Hz, 1H), 6.35 (d, J = 13.6 Hz,
1H), 6.26 (ddd, J = 15.3, 10.8, 1.5 Hz, 1H), 5.79 (dd, J = 15.3, To a solution of vinyl bromide 21 (218 mg, 0.49 mmol,
5.4 Hz, 1H), 5.16 (dd, J = 7.8, 6.4 Hz, 1H), 4.76–4.65 (m, 1H), 1.0 equivalent) in Et2NH (1.2 mL) and benzene (0.4 mL),
3.70 (dd, J = 17.6, 3.1 Hz, 1H), 3.53 (dd, J = 11.5, 7.9 Hz, 1H), Pd(PPh3)4 (17 mg, 0.02 mmol, 3 mol%) was added and the
3.29 (dd, J = 17.6, 8.6 Hz, 1H), 3.04 (dd, J = 11.6, 1.1 Hz, 1H), reaction was stirred for 45 min in the dark. CuI (5 mg,
2.93 (d, J = 4.5 Hz, 1H), 2.36 (dq, J = 13.6, 6.8 Hz, 1H), 1.07 (d, 0.03 mmol, 5 mol%) in a minimum amount of Et2NH was
J = 6.7 Hz, 3H), 0.99 (d, J = 6.9 Hz, 3H); 13C NMR (101 MHz, added followed by dropwise addition of alkyne 5 (117 mg,
CDCl3) δ 203.1, 172.3, 136.7, 134.8, 128.0, 109.6, 71.5, 68.1, 0.49 mmol, 1.0 equiv.) in Et3N (1.0 mL). After 20 h of stirring
45.1, 31.0, 30.8, 19.2, 18.0.
at ambient temperature, the reaction was quenched by the
addition of saturated NH4Cl (15 mL). Et2O (15 mL) was added
and the phases were separated. The aqueous phase was
extracted with Et2O (2 × 15 mL) and the combined organic
(R,4E,6E)-7-Bromo-3-((tert-butyldimethylsilyl)oxy)-1-((S)-
4-isopropyl-2-thioxothiazolidin-3-yl)hepta-4,6-dien-1-one (17)
According to the procedure of Corey and coworkers,31 the layers were dried (Na2SO4), before being concentrated in vacuo.
alcohol 16a was protected with a TBS-group. Yield: 4.2 g (97%); The crude product was purified by column chromatography on
[α]2D0 = 263 (c = 0.5, CHCl3); H NMR (300 MHz, CDCl3) δ 6.69 silica (hexanes–EtOAc 95 : 5) to afford the title compound 22 as
1
(dd, J = 13.4, 10.7 Hz, 1H), 6.31 (d, J = 13.5 Hz, 1H), 6.15 (dd, a pale yellow oil. Yield: 278 mg (95%); TLC (hexanes–EtOAc
J = 15.5, 11.1 Hz, 1H), 5.79 (dd, J = 14.9, 6.6 Hz, 1H), 5.04 (t, J = 9 : 1, CAM stain): Rf = 0.44; [α]2D0 = −15.5 (c = 0.20, MeOH);
7.0 Hz, 1H), 4.75 (q, J = 6.4 Hz, 1H), 3.64 (dd, J = 16.6, 7.8 Hz, 1H NMR (400 MHz, CDCl3) δ 6.51 (dd, J = 15.6, 10.9 Hz, 1H),
1H), 3.47 (dd, J = 10.9, 7.9 Hz, 1H), 3.21 (dd, J = 16.4, 4.6 Hz, 6.19 (dd, J = 15.2, 10.8 Hz, 1H), 5.76 (dd, J = 15.2, 6.0 Hz, 1H),
1H), 3.03 (d, J = 11.6 Hz, 1H), 2.48–2.26 (m, 1H), 1.06 (d, J = 5.58 (dd, J = 15.3, 1.2 Hz, 1H), 5.55–5.47 (m, 1H), 5.45–5.33 (m,
7.2 Hz, 3H), 0.97 (d, J = 7.1 Hz, 3H), 0.86 (s, 9H), 0.05 (s, 3H), 5H), 4.47 (td, J = 6.5, 1.6 Hz, 1H), 4.19 (q, J = 6.3 Hz, 1H), 3.67
0.03 (s, 3H); 13C NMR (75 MHz, CDCl3) δ 202.9, 170.9, 136.8, (s, 3H), 2.82–2.74 (m, 2H), 2.43 (t, J = 7.2 Hz, 2H), 2.40–2.33
127.4, 109.1, 71.8, 69.8, 46.2, 31.0, 30.9, 25.9 (3C), 19.3, 18.2, (m, 4H), 2.33–2.20 (m, 2H), 2.07 (p, J = 7.4 Hz, 2H), 0.97 (t, J =
17.9, −4.2, −4.8.
7.5 Hz, 3H), 0.91 (s, 9H), 0.89 (s, 9H), 0.12 (d, J = 8.3 Hz, 6H),
0.03 (d, J = 8.7 Hz, 6H); 13C NMR (101 MHz, CDCl3) δ 173.7,
141.2, 139.2, 134.4, 129.8, 129.5, 128.7, 128.0, 125.8, 124.1,
110.7, 93.5, 83.5, 72.8, 63.7, 51.7, 36.8, 36.4, 34.2, 26.0
Methyl (R,4Z,7Z,11E,13E)-14-bromo-10-((tert-butyldimethyl-
silyl)oxy)tetradeca-4,7,11,13-tetraenoate (21)
To the Wittig salt 7 (581 mg, 1.04 mmol, 1.0 equiv.) in THF (3C), 26.0 (3C), 25.9, 23.0, 20.9, 18.5, 18.4, 14.4, −4.3 (2C),
(9.5 mL) was added mol. sieves and HMPA (1.5 mL) before −4.6, −4.8. HRMS (TOF ES+): Exact mass calculated for
NaHMDS (0.6 M in toluene, 1.0 equiv.) was slowly added at C35H60O4Si2Na [M + Na]+: 623.3927, found 623.3923.
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Methyl (4Z,7Z,10R,11E,13E,17S,19Z)-10,17-dihydroxydocosa-
4,7,11,13,19-pentaen-15-ynoate (23)
1.9 mL) was added dropwise. The reaction mixture was stirred
at the above-mentioned temperature for 48 h, after which a
saturated solution of NaH2PO4 (4.0 mL) was added. Next, NaCl
(10.0 g) was added followed by EtOAc (50 ml). The organic
phase was decanted, dried (Na2SO4), and concentrated in vacuo
affording the title compound 2 (14 mg, 78%) as a colourless
oil. The chemical purity (>95%) was determined by HPLC
analysis (Eclipse XDB-C18, MeOH–3.3 mM HCOOH in H2O,
7 : 3, 1.0 mL min−1): tr(minor) = 9.97 min and tr(major) =
10.68 min; TLC (hexanes–EtOAc 6 : 4, CAM stain): Rf = 0.03;
[α]2D0 = −24.0 (c = 0.3, MeOH); UV (MeOH) λmax 262, 271,
TBAF (587 mg, 2.25 mmol, 5.0 equiv., 1.0 M in THF) was
added to a solution of TBS-protected alcohol 22 (270 mg,
0.45 mmol, 1.0 equiv.) in THF (6.0 mL) at 0 °C. The reaction
was stirred for 20 h before it was quenched with phosphate
buffer (pH = 7.2, 3.5 mL). Brine (30 mL) and EtOAc (30 mL)
were added and the phases were separated. The water phase
was extracted with EtOAc (2 × 30 mL) and the combined
organic layer was dried (Na2SO4) before being concentrated
in vacuo. The crude product was purified by column chromato-
graphy on silica (hexanes–EtOAc 7 : 3) to afford the title
compound 23 as a pale yellow oil. Yield: 135 mg (81%);
TLC (hexanes–EtOAc 7 : 3, CAM stain): Rf = 0.19; [α]2D0 = −9.2
282 nm. IR (neat) ν = 3316, 3012, 2961, 2930, 1713, 1557 cm−1
;
1H NMR (300 MHz, MeOH-d4) δ 6.52 (dd, J = 14.1, 11.3 Hz,
1H), 6.35–6.19 (m, 2H), 6.08 (dd, J = 11.7, 10.5 Hz, 1H), 5.76
(dd, J = 14.4, 6.5 Hz, 1H), 5.52–5.31 (m, 7H), 4.56 (dt, J = 9.4,
6.8 Hz, 1H), 4.21–4.08 (m, 1H), 2.88–2.78 (m, 2H), 2.42–2.15
(m, 8H), 2.12–2.00 (m, 2H), 0.97 (t, J = 7.5 Hz, 3H); 13C NMR
(126 MHz, CDCl3) δ 177.4, 137.9, 134.9, 134.8, 134.7, 131.4,
131.0, 130.6, 130.0, 129.3, 128.9, 126.5, 125.3, 73.0, 68.6, 36.4,
36.3, 35.3, 26.7, 24.0, 21.7, 14.6. HRMS (TOF ES−): Exact mass
calculated for C22H31O4 [M − H]−: 359.2222, found 359.2213.
All spectroscopic and physical data were in agreement with
those reported in the literature.13b
1
(c = 0.3, MeOH); H NMR (400 MHz, MeOD-d4) δ 6.54 (dd, J =
15.6, 10.8 Hz, 1H), 6.29 (dd, J = 15.2, 10.8 Hz, 1H), 5.82 (dd, J =
15.2, 6.2 Hz, 1H), 5.66 (dd, J = 15.1, 1.8 Hz, 1H), 5.57–5.32
(m, 6H), 4.41 (t, J = 6.7 Hz, 1H), 4.14 (q, J = 6.5 Hz, 1H), 3.66
(s, 3H), 2.87–2.74 (m, 2H), 2.46–2.28 (m, 6H), 2.10 (p, J =
7.4 Hz, 2H), 0.98 (t, J = 7.5 Hz, 3H); 13C NMR (101 MHz,
MeOD-d4) δ 175.3, 142.5, 139.8, 135.3, 131.0, 130.3, 130.3,
129.0, 126.4, 124.7, 111.8, 93.9, 84.3, 72.7, 63.3, 52.1, 36.9,
36.2, 34.8, 26.7, 23.8, 21.7, 14.6. HRMS (TOF ES+): Exact mass
calculated for C23H32O4Na [M + Na]+: 395.2198, found 395.2206.
Methyl (4Z,7Z,10R,11E,13E,15Z,17S,19Z)-10,17-dihydroxy-
do-cosa-4,7,11,13,15,19-hexaenoate (24)
Acknowledgements
The Norwegian Research Council (KOSK II) and The School of
Pharmacy, University of Oslo are gratefully acknowledged for
Ph.D.-scholarships to M. A. and J. E. T., respectively. T. V. H. is
grateful for a Leiv Eriksson travel grant from The Norwegian
Research Council. J. D. is supported by the National Institutes
of Health GM Grant PO1GM095467 (awarded to Charles
N. Serhan). Fruitful discussions with Professor Charles
N. Serhan, Brigham and Women’s Hospital and Harvard
Medical School are gratefully appreciated.
To a solution of alkyne 23 (30 mg, 0.082 mmol) in EtOAc–
pyridine–1-octene (0.83 mL, 10 : 1 : 1) under argon, Lindlar’s
catalyst (10 mg) was added and the flask was evacuated and
filled with argon. The reaction was stirred for 3.5 h at ambient
temperature under a balloon of hydrogen gas until com-
pletion. The reaction mixture was loaded directly onto a silica
gel column and purified by chromatography (hexanes–EtOAc
8 : 2) to afford the title compound 24 as a pale oil. The chemi-
cal purity (>98%) was determined by HPLC analysis (Eclipse
XDB-C18, MeOH–H2O 75 : 25, 1.0 mL min−1): tr(minor) =
12.62 min, and tr(major) = 9.07 min. Yield: 19.5 mg (65%);
TLC (hexanes–EtOAc 6 : 4, CAM stain): Rf = 0.19; [α]2D0 = −22.2
Notes and references
1
1 P. C. Calder, J. Nutr., 2012, 592.
(c = 0.4, MeOH); UV (MeOH) λmax 262, 271, 282 nm. H NMR
2 (a) C. N. Serhan, S. Hong, K. Gronert, S. P. Colgan,
P. R. Devchand, G. Mirick and R. L. Moussignac, J. Exp.
Med., 2002, 196, 1025; (b) P. K. Mukherjee, V. L. Marcheselli,
C. N. Serhan and N. G. Bazan, Proc. Natl. Acad. Sci. U. S. A.,
2004, 101, 8491; (c) A. Ariel, L. Pin-Lan, W. Wang,
W. X. Tang, G. Fredman, S. Hong, K. H. Gotlinger and
C. N. Serhan, J. Biol. Chem., 2005, 280, 43079.
3 (a) C. N. Serhan, R. Yang, K. Martinod, K. Kasuga,
P. S. Pillai, T. F. Porter, S. F. Oh and M. Spite, J. Exp. Med.,
2009, 206, 15; (b) C. N. Serhan, J. Dalli, S. Karamnov,
A. Choi, C. K. Park, Z. Z. Xu, R. R. Ji, M. Zhu and
N. A. Petasis, FASEB J., 2012, 26, 1755.
(400 MHz, MeOD-d4) δ 6.52 (dd, J = 14.0, 10.7 Hz, 1H),
6.33–6.18 (m, 2H), 6.07 (t, J = 11.1 Hz, 1H), 5.76 (dd, J = 14.5,
6.5 Hz, 1H), 5.49–5.32 (m, 7H), 4.56 (dt, J = 8.9, 6.7 Hz, 1H),
4.14 (q, J = 6.5 Hz, 1H), 3.65 (s, 3H), 2.87–2.78 (m, 2H),
2.40–2.29 (m, 7H), 2.25–2.16 (m, 1H), 2.07 (p, J = 7.4 Hz, 2H),
0.97 (t, J = 7.5 Hz, 3H); 13C NMR (101 MHz, MeOD-d4) δ 175.3,
138.0, 134.9, 134.9, 134.7, 131.4, 130.9, 130.5, 130.3, 128.9,
128.9, 126.5, 125.3, 73.0, 68.6, 52.1, 36.4, 36.4, 34.8, 26.7, 23.8,
21.7, 14.6. HRMS (TOF ES+): Exact mass calculated for
C23H34O4Na [M + Na]+: 397.2354, found 397.2365. All spectro-
scopic and physical data were in agreement with those
reported in the literature.13b
4 S. Hong, K. Gronert, P. R. Devchand, R. L. Moussignac and
C. N. Serhan, J. Biol. Chem., 2003, 278, 14677.
Synthesis of protectin D1 (2)
Methyl ester 24 (18 mg, 0.032 mmol) was dissolved in metha-
nol–water 1 : 1 (30 mL) and cooled to 0 °C. LiOH (1.0 M,
5 C. N. Serhan and N. A. Petasis, Chem. Rev., 2011, 111, 5922
and references cited therein.
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Paper
6 C. N. Serhan, K. Gotlinger, S. Hong, Y. Lu, J. Siegelman,
T. Baer, R. Yang, S. P. Colgan and N. A. Petasis, J. Immunol.,
2006, 176, 1848.
7 W. J. Lukiw, J. G. Cui, V. L. Marcheselli, M. Bodker,
A. Botkjaer, K. Gotlinger, C. N. Serhan and N. G. Bazan,
J. Clin. Invest., 2005, 115, 2774.
J. Hammer Andersen and T. V. Hansen, Chem. Phys. Lipids,
2013, 170–171, 41.
15 (a) K. C. Nicolaou, S. E. Webber, J. Ramphal and
Y. Abe, Angew. Chem., 1987, 99, 1077; (b) J. S. Yadav,
P. K. Deshpande and G. V. M. Sharma, Tetrahedron, 1992,
48, 4465.
8 J. M. Calandria, V. L. Marcheselli, P. K. Mukherjee, 16 (a) J. Becher, Org. Synth., 1979, 59, 79; (b) D. Soullez, G. Ple,
J. Uddin, J. W. Winkler, N. A. Petasis and N. G. Bazan,
L. Duhamel and P. Duhamel, J. Chem. Soc., Perkin Trans. 1,
J. Biol. Chem., 2009, 284, 17877.
1997, 1639.
9 V. L. Marcheselli, P. K. Mukherjee, M. Arita, S. Hong, 17 Y. Nagao, W. M. Dai, M. Ochiai, S. Tsukagoshi and
R. Antony, K. Sheets, J. W. Winkler, N. A. Petasis, E. Fujita, J. Org. Chem., 1989, 54, 5211.
C. N. Serhan and N. G. Bazan, Prostaglandins Leukot. Essent. 18 (a) D. A. Evans, J. Barartroli and T. L. Shih, J. Am. Chem.
Fatty Acids, 2010, 82, 27.
10 Y. Zhao, F. Calon, C. Julien, J. W. Winkler, N. A. Petasis,
W. J. Lukiw and N. G. Bazan, PLoS ONE, 2011, 6, e15816.
Soc., 1981, 103, 2127; (b) D. A. Evans, J. M. Takacs,
L. R. McGee, M. D. Ennis, D. J. Mathre and J. Bartroli, Pure
Appl. Chem., 1981, 53, 1109.
11 (a) Z. Z. Xu, X. J. Liu, T. Berta, C. K. Park, N. Lü, 19 (a) M. Romero-Ortega, D. A. Colby and H. F. Olivo, Tetra-
C. N. Serhan and R. R. Ji, Ann Neurol., 2013, 74, 490;
(b) M. Morita, K. Kuba, A. Ichikawa, M. Nakayama,
hedron Lett., 2002, 43, 6439; (b) R. Tello-Aburto, A. Ochoa-
Teran and H. F. Olivo, Tetrahedron Lett., 2006, 47, 5915.
J. Katahira, R. Iwamoto, T. Watanebe, S. Sakabe, T. Daidoji, 20 E. J. Corey, H. Cho, C. Rücker and D. H. Hua, Tetrahedron
S. Nakamura, A. Kadowaki, T. Ohto, H. Nakanishi, Lett., 1981, 22, 3455.
R. Taguchi, T. Nakaya, M. Murakami, Y. Yoneda, H. Arai, 21 D. Seebach, G. Adam, R. Zibuck, W. Simon, M. Rouilly,
Y. Kawaoka, J. M. Penninger, M. Arita and Y. Imai, Cell,
2013, 153, 112.
12 (a) C. N. Serhan and N. Chiang, Br. J. Pharmacol., 2008,
W. L. Meyer, J. F. Hinton, T. A. Privett, G. E. Templeton,
D. K. Heiny, U. Gisi and H. Binder, Liebigs Ann. Chem.,
1989, 1233.
153, S200; (b) C. N. Serhan and N. Chiang, Curr. Opin. 22 R. Appel, Angew. Chem., Int. Ed. Engl., 1975, 14, 801.
Pharmacol., 2013, 13, 632.
13 (a) N. Ogawa and Y. Kobayashi, Tetrahedron Lett., 2011, 52,
23 K. Sonogashira, Y. Tohda and N. Hagihara, Tetrahedron
Lett., 1975, 16, 4467.
3001; (b) N. A. Petasis, R. Yang, J. W. Winkler, M. Zhu, 24 H. Lindlar, Helv. Chim. Acta, 1952, 35, 446.
J. Uddin, J. N. G. Bazan and C. N. Serhan, Tetrahedron Lett., 25 E. J. Corey and B. B. Snider, J. Am. Chem. Soc., 1972, 94, 6190.
2012, 53, 1695.
26 (a) K. C. Nicolaou, T. Ladduwahetty, I. M. Taffer and
R. E. Zipkin, Synthesis, 1986, 344; (b) L. E. Overman and
A. S. Thompson, J. Am. Chem. Soc., 1988, 110, 2248.
14 (a) T. V. Hansen and Y. Stenstrøm, Synth. Commun., 2000,
30, 2549; (b) T. V. Hansen and Y. Stenstrøm, Tetrahedron:
Asymmetry, 2001, 12, 1407; (c) T. V. Hansen and 27 D. J. Pasto and R. T. Taylor, Org. React., 1991, 40, 91.
L. Skattebøl, Tetrahedron Lett., 2004, 45, 2809; (d) H. F. Anwar 28 W. Boland, N. Schroer, C. Sieler and M. Feigel, Helv. Chim.
and T. V. Hansen, Org. Lett., 2009, 11, 587; (e) A. Vik,
T. V. Hansen, A. K. Holmeide and L. Skattebøl, Tetrahedron 29 N. Chiang, G. Fredman, F. Bäckhed, S. F. Oh, T. Vickery,
Lett., 2010, 51, 2852; (f) M. A. Yasser and T. V. Hansen, Pure B. A. Schmidt and C. N. Serhan, Nature, 2012, 484, 524.
Appl. Chem., 2011, 83, 489; (g) M. A. Yasser and 30 C. N. Serhan, G. Fredman, R. Yang, S. Karamnov,
Acta, 1987, 70, 1025.
T. V. Hansen, Tetrahedron Lett., 2011, 52, 1057; (h) A. Vik
and T. V. Hansen, Tetrahedron Lett., 2011, 52, 1060;
L. S. Belayev, N. G. Bazan, M. Zhu, J. W. Winkler and
N. A. Petasis, Chem. Biol., 2011, 18, 976.
(i) M. G. Jakobsen, A. Vik and T. V. Hansen, Tetrahedron 31 E. J. Corey, H. Cho, C. Rucker and D. H. Hua, Tetrahedron
Lett., 2012, 53, 5837; ( j) M. A. Yasser, A. Vik, T. Hofer,
Lett., 1981, 22, 3455.
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